The present disclosure relates to an organic electroluminescent element, a display apparatus, and a manufacturing method of the organic electroluminescent element.
An organic electroluminescent element (a so-called organic EL element) is a self light-emitting-type element having a light-emitting layer containing an organic compound between an anode and a cathode. In such an organic electroluminescent element, when a voltage is applied between an anode and a cathode, holes injected from an anode move to a light-emitting layer through a hole transport layer, while electrons injected from a cathode move to the light-emitting layer through an electron transport layer. Then, recombination of the holes and electrons that have moved to the light-emitting layer generates an exciton, and transition of the generated exciton to a ground state causes light-emitting to occur.
Here, it is desired that the organic electroluminescent element used as a light source of a display apparatus and a lighting apparatus have high light-emitting efficiency.
For example, JP 2003-272860A, JP 2010-15787A and JP 2005-267990A disclose a technique of adopting a multi-stack structure in which a plurality of light-emitting units is laminated to each other through a charge generating layer in the organic electroluminescent element in order to improve light-emitting efficiency.
However, in the organic electroluminescent element having the multi-stack structure, while current efficiency can be improved by laminating a plurality of light-emitting units, an applied voltage causes a light-emitting balance of the units to change, resulting in a change in color taste of the light.
To address this concern, JP 2010-129301A discloses a technique of controlling the arrangement order of the light-emitting layers based on the light-emitting peak wavelength so that a light-emitting layer farther from an anode has a higher highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), thereby to suppress the change in color taste of emitted light.